In Remington's Pharmaceutical Sciences, 14th, Ed., p 1681, published in 1970, it was reported that pill coating has been a pharmaceutical technique for well over ten centuries. For example, Rhazes (850-932 A.D.) used mucilage, a seaweed substance, for coating pills in the ninth century, and Avicenna (980-1037 A.D.) is credited with the introduction of silver and gold pill coatings into medicine. The coating of pills with finely powdered talcum, called pearl coating, was popular in previous times. Gelatin coating of pills was introduced into medicine by Garot in 1838. The first sugar-coated pills in the United States were imported from France in about 1842. The first sugar-coated pill was manufactured in the United States in 1856 by Warner, a Philadelphia pharmacist. In about 1884 Unna introduced enteric coated pills.
Unique pharmaceutically-acceptable tablets, manufactured as an osmotic dosage form entered the fields of medicine and pharmacy with the invention of osmotic dosage forms by inventors Theeuwes and Higuchi in U.S. Pat. Nos. 3,845,770 and 3,916,899. The osmotic dosage forms disclosed in these patents comprise a semipermeable membrane that surrounds a compartment containing a therapeutic agent. The membrane is permeable to the passage of an external fluid, and it is impermeable to the passage of drug. There is at least one exit through the membrane for delivering the therapeutic agent from the osmotic dosage form.
A pioneering advancement in osmotic dosage forms was made available to the drug dispensing arts in U.S. Pat. No. 4,327,725 by patentees Cortese and Theeuwes. The invention provided by these inventors concerned an osmotic dosage form for delivering a therapeutic agent, that because of its solubility, is difficult to deliver in therapeutic amounts at a controlled rate over time. The dosage form of U.S. Pat. No. 4,327,725 comprises a semipermeable wall that surrounds a therapeutic agent and an expandable agent. In operation, the expandable agent in the presence of imbibed fluid, expands and pushes the therapeutic agent through an exit passageway from the dosage form.
While the above presented dosage forms are useful for the management of health and disease, a serious disadvantage is associated with their manufacture. That is, the prior art used two or more solvents to dissolve a coating-forming membrane and a flux enhancer, because one solvent does not dissolve both the membrane and the flux enhancer. A typical solvent system used by the prior ad for this purpose comprises two or more organic solvents, often possessing degrees of unknown incompatibility. Further, the prior art solvents often produced high-flux membranes that exhibited mechanical defects, which lead to weakened membranes accompanied by brittleness. Then too, the use of multiple solvent can produce haziness or opacity in a membrane, which makes it impossible to identify selected regions of a dosage form. Also, the use of multiple organic solvents presents an environmental problem as the solvents require complicated recover systems to avoid contaminating the environment, which recovery systems are expensive to install and to operate.
It will be appreciated by those skilled in the drug dispensing art, that if a coating is provided that comprises a single solvent and its substantively-free of excessive organic solvent for coating dosage forms, such a coating and its accompanying solvent would have an immediate positive value, and concomitantly, represent an advancement in the drug coat and drug coating art. Likewise, it will be appreciated by those versed in the coat and process-coating arts, that if a coat and a process for coating are made available for dosage forms that overcome the disadvantages known to the prior art, they would have a practical application in the fields of medicine and pharmacy.